全文获取类型
收费全文 | 741篇 |
免费 | 57篇 |
国内免费 | 1篇 |
专业分类
林业 | 56篇 |
农学 | 5篇 |
基础科学 | 3篇 |
148篇 | |
综合类 | 137篇 |
农作物 | 13篇 |
水产渔业 | 27篇 |
畜牧兽医 | 347篇 |
园艺 | 21篇 |
植物保护 | 42篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 11篇 |
2013年 | 43篇 |
2012年 | 42篇 |
2011年 | 55篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 43篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 36篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 31篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 4篇 |
排序方式: 共有799条查询结果,搜索用时 234 毫秒
111.
112.
B M Jayarao B E Gillespie M J Lewis H H Dowlen S P Oliver 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1999,46(7):433-442
From 1987 to 1991, almost 36,000 quarter samples of mammary secretion representing 1790 lactations of 510 dairy cows from a research herd were collected for bacteriological examination. The percentage of cows infected with Streptococcus uberis ranged from 12 to 16% of cows/year. S. uberis was isolated from 14.2% of lactations over the 5-year period. The prevalence of S. uberis intramammary infection (IMI) was significantly higher in cows with > or = 4 lactations than in cows with 3 or fewer lactations. Regardless of lactation number, the prevalence of S. uberis was highest before parturition, during early lactation and near drying off. The prevalence of S. uberis infected quarters ranged from 1.3 to 2.3% of quarters/year; the prevalence rate for the 5-year period was 2% of quarters. The quarter prevalence of S. uberis was lowest in cows with < or = 3 lactations, increased significantly with lactation number and was highest in cows with > or = 6 lactations. The percentage of quarters infected with S. uberis varied significantly by year. The majority (95%) of S. uberis IMI were subclinical. The ratio of subclinical IMI to clinical IMI was lowest during early lactation, and increased with days in milk, and with lactation age except for cows in their 5th and 6th lactations. Results of this epidemiological investigation suggest that opportunities exist where suitable control measures could be applied to reduce the impact of S. uberis infections in the dairy herd. 相似文献
113.
Feeding ragworm (Nereis virens Sars) to common sole (Solea solea L.) alleviates nutritional anaemia and stimulates growth 下载免费PDF全文
Jeroen Kals Robbert J W Blonk Arjan P Palstra Tim K Sobotta Fulvio Mongile Oliver Schneider Josep V Planas Johan W Schrama Johan A J Verreth 《Aquaculture Research》2017,48(3):752-759
Common sole fed with commercial pellets develop anaemia and are restricted in their growth performance. The anaemia can be the result of a difference in feed intake, a nutritional deficiency, an inflammatory response to infection or combinations of these aspects. In this study, it was investigated whether feeding ragworm would alleviate the anaemia and stimulate growth. Sole were fed one of three diets: a commercial feed, a commercial feed treated with ragworm extract or chopped ragworm. By comparing groups, three hypotheses were tested: (1) feeding ragworm alleviates the anaemia and positively affectS the sole's metabolic performance reflected in feed intake, feed efficiency and growth; (2) anaemia is alleviated by a higher feed intake when feeding ragworm and (3) anaemia is caused by an inflammatory response to infection. The sole fed with a commercial diet suffered from anaemia. Feeding sole with ragworm alleviated the anaemia as the average haematocrit level nearly doubled in these fish as compared to fish fed pellets. Investigation of the expression of genes in the liver indicated that the anaemia in sole fed pellets is a nutritional anaemia and not an anaemia due to an inflammatory response. Sole fed ragworm showed improved growth which may be a consequence of the higher haematocrit levels in these fish increasing their oxygen carrying capacity. Addition of ragworm extract to the pellets levelled the feed intake between pellets and ragworm, but did not improve the anaemic state of sole and had only a limited effect on growth. 相似文献
114.
Rohan J. C. Currey Stephen M. Dawson Elisabeth Slooten Karsten Schneider David Lusseau Oliver J. Boisseau Patti Haase Jamelia A. Williams 《水产资源保护:海洋与淡水生态系统》2009,19(6):658-670
- 1. The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the southern limit of the species' range, exposed to impacts from tourism and habitat modification. Patterns in apparent annual survival were analysed from photographic resightings of naturally marked adults (1990 to 2008) and calves within the first year of life (1994 to 2008) using capture‐recapture models.
- 2. The most parsimonious model for adults provided a time‐invariant, sex‐invariant estimate of survival (?a(1990–2008)=0.9374; 95% CI: 0.9170–0.9530), marginally lower than prior estimates for wild bottlenose dolphins.
- 3. The most parsimonious model for calves indicated a significant time‐variant decline in survival from an estimate similar to other populations (?c(1994–2001)=0.8621; 95% CI: 0.6851–0.9473) to a current estimate that is, to our knowledge, the lowest recorded for free‐ranging bottlenose dolphins (?c(2002–2008)=0.3750; 95% CI: 0.2080–0.5782).
- 4. Information theoretic evidence ratios suggested that observed patterns in calf survival were 22 times more likely to be explained by a decline coincident with the opening of a second tailrace tunnel for a hydroelectric power station than by a decline in any other year or across multiple years.
- 5. Projections using an age‐structured stochastic population model indicated that the current level of calf survival was unsustainable (population decline: 100% of model runs; population extinction: 41.5% of model runs) and was a key factor in the observed population decline in Doubtful Sound.
115.
The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole,Solea solea (L.) 下载免费PDF全文
Stephan S W Ende Saskia Kroeckel Johan W Schrama Oliver Schneider Johan A J Verreth 《Aquaculture Research》2017,48(9):4696-4706
This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (kgCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (kgGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg?0.8 day?1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g?0.8 day?1. The gross energy maintenance requirement of large common sole was 25 kJ g?0.8 day?1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization. 相似文献
116.
The aerial application of pesticides increased rapidly following the end of the Second World War, as, along with the development of a wider range of synthetic pesticides, more planes and pilots became available. It also became clear that new and previously inaccessible areas could be sprayed from the air. By the 1980s there were around 100 planes in the United Kingdom (UK) capable of spraying pesticides. However, increasing environmental pressure brought about the introduction of tougher legislation to control pesticide usage. The Food and Environment Protection Act 1985 and the Control of Pesticides Regulations 1986 (as amended) introduced tight controls over the application of pesticides from the air. Aerial application of pesticides has been monitored each year by the UK Ministry of Agriculture, Fisheries and Food (MAFF) since 1978, during which time the area treated has decreased significantly. This has been partly as a result of changes in legislation but also due to technological improvements in conventional crop‐protection methods. The area treated from the air in the UK has never risen above 2.5% of the area treated from the ground and in 1998 had fallen to less than 0.04% of the total area treated with pesticides. It is likely that this figure will continue to fall in the future. By 1998, the only pesticides to be sprayed from the air comprised fungicides, herbicides and insecticides. As a group, herbicides comprised the greatest area of treatment and the only target to show an increase in area treated in recent years has been bracken (Pteridium aquilinum (L) Kuhn). © Crown copyright 2000. Reproduced with the permission of Her Majesty's Stationery Office. 相似文献
117.
Frederick Feyrer Matthew Young Oliver Patton David Ayers 《Ecology of Freshwater Fish》2020,29(2):188-196
Clear Lake Hitch is an imperilled minnow endemic to Clear Lake, Lake County, California, United States listed as threatened under the California Endangered Species Act (ESA) and a candidate for listing under the United States ESA. It exhibits a potamodromous life cycle whereby adults, which reach up to 6 + years in age and over 350 mm in length, migrate into Clear Lake's ephemeral tributaries briefly during spring to spawn. Conservation and management of Clear Lake Hitch is inhibited, in part, by a lack of information on the lacustrine habitat of nonbreeding individuals within Clear Lake. To address this problem, we sampled Clear Lake Hitch with gill nets in a stratified random sampling design to determine the distribution and habitat associations in early summer 2017 and 2018. We identified abundance-habitat relationships for juveniles and adults using Bayesian zero-inflated negative binomial generalised linear mixed modelling. Results indicated that dissolved oxygen concentration was the most important habitat feature measured; juveniles and adults were substantially more abundant in normoxic (≥2 mg/l) than in hypoxic (<2 mg/l) habitat. Both also exhibited weak positive relationships with chlorophyll fluorescence, suggesting relatively productive habitats may support higher numbers of Clear Lake Hitch. Spatially, juveniles were most abundant in nearshore habitats while adults were ubiquitous, indicating an ontogenetic habitat expansion that may be associated with a resource availability-predation risk trade-off. Management actions undertaken to improve hypoxia problems in Clear Lake would also improve Clear Lake Hitch habitat. 相似文献
118.
Ntsane Moleleki Michael J. Wingfield Brenda D. Wingfield Oliver Preisig 《European journal of plant pathology / European Foundation for Plant Pathology》2011,131(2):261-268
A 4.1 kbp positive-strand RNA virus known as Diaporthe RNA virus 1 (DRV1) occurs in hypovirulent, non-sporulating isolates
of the fungal pathogen Diaporthe perjuncta. A full-length cDNA clone of DRV1 was developed and RNA transcribed from the cDNA clone used to transfect different Diaporthe spp. The transfected species included three D. ambigua isolates and an unidentified Phomopsis asexual state of a Diaporthe sp. Successful transfections were confirmed using RT-PCR. Although the in vitro-transcribed positive sense single-stranded
RNA used for transfection included vector sequences at both ends, the genomes of progeny virus from DRV1-transfected isolates
were free of the vector sequences. Transfection resulted in morphological changes in these fungal pathogens. However, the
presence of DRV1 did not reduce growth rate in two of the three D. ambigua or the Phomopsis sp. significantly. Pathogenicity studies showed that the transfected isolates have reduced aggresiveness. 相似文献
119.
Van Sinh Nguyen Hung Manh Nguyen Anika Klotzbücher Doris Vetterlein Thimo Klotzbücher Reinhold Jahn Janina Schneiker Manfred Türke Oliver Fried Erwin Bergmeier Cornelia Sattler Josef Settele 《Paddy and Water Environment》2018,16(2):353-358
Two major human-made problems in rice production systems in the north of Vietnam concern the low plant-available silicon content of soils and the low biodiversity. The results of the LEGATO project suggest a change to an environmentally friendly rice production system that will help to recover biodiversity. We propose here a framework for a demonstration and dissemination model that will be exemplary for the farmers once it has been successfully realized. We advocate local-option models in different districts to demonstrate to farmers. The methods should be adapted to local and ecoregional differences in climate and land-use tradition, and they explicitly take into account soil care, organic fertilizer, manual weeding, native nectar-rich plant bunds, manual pest snail collection, hymenopteran nesting aids, and biodiversity and yield monitoring. 相似文献
120.